The present invention relates to an image forming apparatus and, more particularly, to an image forming apparatus such as an electronic copying machine, a digital copying machine (PPC), a printer or a facsimile for forming an image of a document on a cut sheet serving as an image forming medium, in which the image of the document can be formed at a correct position by correcting lateral misalignment of the cut sheet serving as the image forming medium which is supplied and fed to an image forming unit, and a method for controlling the image forming apparatus.
As is well known, the image forming apparatus such as an electronic copying machine, a digital copying machine (PPC), a printer or a facsimile is designed such that an image of a document can be formed on a cut sheet serving as an image forming medium which is supplied and fed to an image forming unit provided with a laser printer.
In this case, if there is lateral misalignment of the cut sheet fed to the image forming unit, the image of the document cannot be formed at a correct position on the cut sheet.
Such lateral misalignment is liable to become large in the case where the cut sheet is fed in a direction perpendicular to the width direction of the cut sheet.
In view of this, in an electrophotographic printing apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-210285, there is provided a sheet edge sensor consisting of an array of light emitting elements and an array of light receiving elements arranged along the entire width in a direction perpendicular to a sheet feeding direction on a sheet feeding path, i.e., in a lateral direction of the sheet, for detecting misalignment in the direction of the width of the sheet, such that a laser printer in an image forming unit is controlled based on the detection result, thus correcting a position at which an electrostatic latent image is formed on a photosensitive drum.
In this manner, when the electrostatic latent image formed on the photosensitive drum is transferred onto a cut sheet serving as an image forming medium with a toner, a correct image of a document without any misalignment can be formed even on the cut sheet serving as the image forming medium having lateral misalignment.
However, since the sheet edge sensor consisting of the array of the light emitting elements and the array of the light receiving elements arranged along the entire width in the direction perpendicular to the sheet feeding direction on the sheet feeding path, i.e., in the lateral direction of the sheet is used as a sensor element in the above-described prior art, the sensor is redundantly configured such that the sensor elements are arranged even at portions where the cut sheet serving as the image forming medium having a size previously designated by a user is not actually fed.
There arise problems of much waste and an increase in cost by using the sheet edge sensor having the redundant configuration in which the sensor elements are arranged even at the portions where the cut sheet having the designated size is not actually fed.
Furthermore, if there is a smear caused by sheet leavings on the feeding path at the portion at which the sheet edge sensor is disposed, the conventional sheet edge sensor may erroneously detect the sheet at that portion.
Moreover, if a portion colored with a smear or the like is judged on a white-and-black criterion in the case where the conventional sheet edge sensor is a reflection type detecting sensor, the sensor may erroneously judge that a white sheet partly colored with a smear or the like is black as a whole.
Additionally, the image forming unit provided with the laser printer may over-correct the misalignment in the case where the conventional sheet edge sensor cannot detect a sheet edge for some accidental reasons, or the detection result differs greatly from the actual misalignment.
An object of the present invention is to provide an image forming apparatus capable of correcting lateral misalignment in such a manner that a correct image of a document without any misalignment can be formed even on a cut sheet serving as an image forming medium having lateral misalignment, by means of an inexpensive and compact sheet edge sensor mechanism by detecting the edge of the cut sheet serving as the image forming medium by the use of sensor elements separately arranged at portions at which the sensor elements are actually used according to the size of the cut sheet serving as the image forming medium, and a method for controlling the image forming apparatus.
Another object of the present invention is to provide an image forming apparatus capable of correcting lateral misalignment in such a manner that a correct image of a document without any misalignment can be formed even on a cut sheet serving as an image forming medium having lateral misalignment, by means of an inexpensive and compact sheet edge sensor mechanism, by detecting the edge of the cut sheet serving as the image forming medium by the use of a sensor element movably arranged at a portion at which the sensor element is actually used according to the size of the cut sheet serving as the image forming medium, and a method for controlling the image forming apparatus.
In this case, it is to be understood that the sensor elements are arranged not only in the direction of the width of the sheet but also at portions requiring accuracy.
Furthermore, according to the present invention, a judgment criterion is previously corrected based on the current state of the sensor, thereby reducing erroneous detection.
Moreover, according to the present invention, a mechanism for removing a smear on the glass stage on which a document is placed can be eliminated, thereby achieving cost reduction as a whole.
Additionally, according to the present invention, information on the color of the sheet to be used is previously acquired, and thus, a judgment criterion corresponding to the color is used, thereby eliminating erroneous detection caused by a difference in color of the sheet.
In addition, according to the present invention, there is provided a limitation in the case where misalignment exceeds an estimated value, thereby minimizing over-correction.
In order to achieve the above-described objects, according to the present invention:
(1) There is provided an image forming apparatus comprising:
a sheet feeding unit provided with a feeding path, on which a cut sheet serving as an image forming medium having a predetermined size is fed;
a sheet edge sensor having sensor elements separately arranged at portions, at which the edge of the cut sheet serving as the image forming medium having the predetermined size can be detected, along a direction perpendicular to the feeding direction of the cut sheet serving as the image forming medium on the feeding path in the sheet feeding unit;
an image forming unit for forming a predetermined image on the cut sheet serving as the image forming medium to be fed by the sheet feeding unit; and
an image formation correcting unit for correcting image formation according to lateral misalignment of the cut sheet serving as the image forming medium based on a detection result transmitted from the sheet edge sensor when a predetermined image is formed on the cut sheet serving as the image forming medium by the image forming unit.
In order to achieve the above-described objects, according to the present invention:
(2) There is provided an image forming apparatus according to (1), wherein when the presence of the sheet is detected based on the detection result transmitted from the sheet edge sensor, the image formation correcting unit adjusts a threshold as a judgment criterion of the presence of the sheet before actual detection of the sheet by the sheet edge sensor.
In order to achieve the above-described objects, according to the present invention:
(3) There is provided an image forming apparatus according to (2), wherein when the presence of the sheet is detected based on the detection result transmitted from the sheet edge sensor, the image formation correcting unit previously designates the color of the sheet, and then, resets the threshold as the judgment criterion of the presence of the sheet in accordance with the designated color.
In order to achieve the above-described objects, according to the present invention:
(4) There is provided an image forming apparatus according to (1), wherein when the amount of lateral misalignment of the sheet is corrected based on the detection result transmitted from the sheet edge sensor, the image formation correcting unit judges as to whether or not the detected amount of misalignment exceeds a predetermined value, and then, gives a limitation to correction of the lateral misalignment of the sheet in the case where the detected amount of misalignment exceeds the predetermined value.
In order to achieve the above-described objects, according to the present invention:
(5) There is provided an image forming apparatus comprising:
a sheet feeding unit provided with a feeding path, on which a cut sheet serving as an image forming medium having a predetermined size is fed;
a sheet edge sensor having a sensor element movably arranged at a portion, at which the edge of the cut sheet serving as the image forming medium having the predetermined size can be detected, along a direction perpendicular to the feeding direction of the cut sheet serving as the image forming medium on the feeding path in the sheet feeding unit;
an image forming unit for forming a predetermined image on the cut sheet serving as the image forming medium to be fed by the sheet feeding unit; and
an image formation correcting unit for correcting image formation according to lateral misalignment of the cut sheet serving as the image forming medium based on a detection result transmitted from the sheet edge sensor when a predetermined image is formed on the cut sheet serving as the image forming medium by the image forming unit.
In order to achieve the above-described objects, according to the present invention:
(6) There is provided an image forming apparatus according to (5), wherein when the presence of the sheet is detected based on the detection result transmitted from the sheet edge sensor, the image formation correcting unit adjusts a threshold as a judgment criterion of the presence of the sheet before actual detection of the presence of the sheet by the sheet edge sensor.
In order to achieve the above-described objects, according to the present invention:
(7) There is provided an image forming apparatus according to (6), wherein when the presence of the sheet is detected based on the detection result transmitted from the sheet edge sensor, the image formation correcting unit previously designates the color of the sheet, and then, resets the threshold as the judgment criterion of the presence of the sheet in accordance with the designated color.
In order to achieve the above-described objects, according to the present invention:
(8) There is provided an image forming apparatus according to (5), wherein when the amount of lateral misalignment of the sheet is corrected based on the detection result transmitted from the sheet edge sensor, the image formation correcting unit judges as to whether or not the detected amount of misalignment exceeds a predetermined value, and then, gives a limitation to correction of the lateral misalignment of the sheet in the case where the detected amount of misalignment exceeds the predetermined value.
In order to achieve the above-described objects, according to the present invention:
(9) There is provided a method for controlling an image forming apparatus comprising the steps of:
feeding a cut sheet serving as an image forming medium having a predetermined size along a feeding path provided in a sheet feeding unit;
separately arranging sensor elements constituting a sheet edge sensor at portions, at which the edge of the cut sheet serving as the image forming medium having the predetermined size can be detected, along a direction perpendicular to the feeding direction of the cut sheet serving as the image forming medium on the feeding path in the sheet feeding unit;
forming a predetermined image on the cut sheet serving as the image forming medium to be fed to an image forming unit by the sheet feeding unit; and
correcting image formation according to lateral misalignment of the cut sheet serving as the image forming medium based on a detection result transmitted from the sheet edge sensor when a predetermined image is formed on the cut sheet serving as the image forming medium by the image forming unit.
In order to achieve the above-described objects, according to the present invention:
(10) There is provided a method for controlling an image forming apparatus according to (9), wherein when the presence of the sheet is detected based on the detection result transmitted from the sheet edge sensor, a threshold as a judgment criterion of the presence of the sheet is adjusted in the image formation correcting step before actual detection of the presence of the sheet by the sheet edge sensor.
In order to achieve the above-described objects, according to the present invention:
(11) There is provided a method for controlling an image forming apparatus according to (10), wherein when the presence of the sheet is detected based on the detection result transmitted from the sheet edge sensor, the color of the sheet is previously designated, and then, the threshold as the judgment criterion of the presence of the sheet is reset in accordance with the designated color in the image formation correcting step.
In order to achieve the above-described objects, according to the present invention:
(12) There is provided a method for controlling an image forming apparatus according to (9), wherein when the amount of lateral misalignment of the sheet is corrected based on the detection result transmitted from the sheet edge sensor, it is judged as to whether or not the detected amount of misalignment exceeds a predetermined value, and then, a limitation is given to correction of the lateral misalignment of the sheet in the case where the detected amount of misalignment exceeds the predetermined value in the image formation correcting step.
In order to achieve the above-described objects, according to the present invention:
(13) There is provided a method for controlling an image forming apparatus comprising the steps of:
feeding a cut sheet serving as an image forming medium having a predetermined size along a feeding path provided in a sheet feeding unit;
moving a sensor element constituting a sheet edge sensor at a portion, at which the edge of the cut sheet serving as the image forming medium having the predetermined size can be detected, along a direction perpendicular to the feeding direction of the cut sheet serving as the image forming medium on the feeding path in the sheet feeding unit;
forming a predetermined image on the cut sheet serving as the image forming medium to be fed to an image forming unit by the sheet feeding unit; and
correcting image formation according to lateral misalignment of the cut sheet serving as the image forming medium based on a detection result transmitted from the sheet edge sensor when a predetermined image is formed on the cut sheet serving as the image forming medium by the image forming unit.
In order to achieve the above-described objects, according to the present invention:
(14) There is provided a method for controlling an image forming apparatus according to (13), wherein when the presence of the sheet is detected based on the detection result transmitted from the sheet edge sensor, a threshold as a judgment criterion of the presence of the sheet is adjusted in the image formation correcting step before actual detection of the presence of the sheet by the sheet edge sensor.
In order to achieve the above-described objects, according to the present invention:
(15) There is provided a method for controlling an image forming apparatus according to (14), wherein when the presence of the sheet is detected based on the detection result transmitted from the sheet edge sensor, the color of the sheet is previously designated, and then, the threshold as the judgment criterion of the presence of the sheet is reset in accordance with the designated color in the image formation correcting step.
In order to achieve the above-described objects, according to the present invention:
(16) There is provided a method for controlling an image forming apparatus according to (13), wherein when the amount of lateral misalignment of the sheet is corrected based on the detection result transmitted from the sheet edge sensor, it is judged as to whether or not the detected amount of misalignment exceeds a predetermined value, and then, a limitation is given to correction of the lateral misalignment of the sheet in the case where the detected amount of misalignment exceeds the predetermined value in the image formation correcting step.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.